January 17, 2015

Small Batch Mash Tun Redesign

My original small batch mash tun used a two gallon cooler with a grain bag to gain the convenience of BIAB with all the temperature regulation of a cooler mash tun. While I have been reasonably happy with the design from a temperature regulation vantage point, I have been dissatisfied with the  volume of trub ending up in the fermentation vessel after the boil. I know this is a problem across the board with BIAB and for a larger fermentation vessel it isn't a problem. Using five liter jugs as I do, space is at a premium to ensure sufficient headspace so I do not lose beer due to blowoff. So reducing the trub is an important goal.

To remedy this problem I have adopted a modification of the typical cooler design employing a toilet line braid that is located around the internet and the same design I have on my ten gallon cooler mash tun. It's an easy system with parts readily available at any big box hardware store and this particular design can be put together for about $7. I am sure more enterprising brewers could fashion a nicer set up but for my purposes this is sufficient to reduce the trub. If you are familiar with the typical design then  you know it is the stainless steel braided line for a toilet intake line attached to a ball valve where the original plastic spigot was. For this version I left the original spigot intact. On a larger cooler the hot runnings will heat up that plastic spigot to the point it is uncomfortable to hold open and you really don't want to have to sit and hold the spigot open for all that time. On the two gallon cooler the spigot opens by pulling away from the liquid so there is no concern about holding uncomfortably hot plastic and draining a mash tun of this size isn't much of a time concern.


  • 1/2" stainless steel pipe clamp screw fastener
  • 3/8" stainless steel pipe clamp screw fastener
  • 3/8" brass pipe plug (Watts LFA-737)
  • 3/8" toilet supply line (get the shortest one you can find)


  • Hacksaw
  • Standard screwdriver
  • Needle nose pliers
The first thing you want to do is take apart the spigot assembly on the cooler. It will be easier to attach the braid to the assembly that way. The assembly is easy to disassemble.

First unscrew the outside piece by turning it counterclockwise until it slides out.

Next do the same for the interior piece.

Third, reach inside the cooler and push out the middle piece of the assembly. It should slide right out.

Fourth, remove the gasket on the inside.

If you have used this cooler yourself you may find the pieces have some mold growth. Now is a good time to clean those parts. It is also good evidence that with these plastic and rubber pieces you need to disassemble the cooler like this and clean all the parts every brew or two.

Fifth, use a hack saw to cut off both ends of the toilet supple line. Discard the end pieces. If you did a rough job with the cuts you can clean it up with wire cutters, if you have some, or just leave it messy. Your beers won't care. Once you can the ends cut off, use needle nose pliers to remove the vinyl tubing inside. Discard this as well.

Sixth, insert the plug threaded side in to the braided line so the non-threaded end is exposed. Then use the 3/8" fastener to hold the plug in place. The plug keeps the end of the braid sealed so grain bits can't get through. It also helps weigh down the end so the braid doesn't float on top of the mash. (see the next two pics)

Here comes the fun part. Go ahead and slide the other fastener onto the braid and it slide all the way to the end with the plug. You need to make this 3/8" braid fit on the outside of this 1/2" spigot assembly. The braid needs to be stretched out. The easiest way to this is to insert the needle nose pliers in the braid and pull the handles away from each other. You need to do this quite a bit and rotate the braid so you get a larger hole. It need to fit on the outside of the second piece you removed from the spigot assembly. It is easiest to put the pliers all the way in and expand the braid and then move them out an inch, do the same and keep repeating until you are expanding the last inch of the braid. Eventually the braid will give up and the hole will expand. Force the braid onto the inner end of the spigot assembly and fasten it as tight as you can (without breaking the plastic) with the fastener. You may find the braid is sloppy after this work with some awkward holes. Roll the braid between your hands (or your fingers) to lengthen it and diminish the diameter, sort of like how as a kid you would roll out snakes out of playdoh.

Last, reassemble the spigot assembly. The middle piece with the male adapter slides in first from the outside. There are three notches on the outside of the cooler that need to line up with this piece. Then slide the washer back into place on the inside of the cooler. There is a small lip on the washer that faces towards the outside of the cooler. At this point don't worry about getting it lined up perfectly, just get it over the threads. Then screw in the outside piece. Now make sure the washer lines up correctly and seals the inside. Finally, screw in the last piece with your braid.

This took me about fifteen minutes, which included writing the blog while I was putting it together. It isn't magnificently attractive but it does the job and doesn't destroy the normal use of the cooler.


  1. Great! So, I'm having a similar small batch problem (getting a "clean", but "efficient" sparge). Now that you've modified your cooler for sparging ... will you change your BIAB method and mash directly in your cooler?

  2. Yeah, I've gone to mashing directly in the cooler with no bag. At first I thought I'd use the bag in the cooler like a second filter but I found the bag interfered with the grain laying on the braid and acting as a filter so I was getting almost as much trub that way. I've since ditched the bag entirely and now I'm getting really clean wort out of the mash.